Perfluoropolyethers are products known in the technique. The preparation thereof is described in particular in British Pat. Nos. 1,104,482, 1,153,306, 1,189,337, 1,217,871 and in U.S. Pat. No. 3,242,218.
From British Pat. No. 1,226,566 it is known how to neutralize the abovesaid end groups by reaction with fluorine at temperatures ranging from 50.degree. to 250.degree. C., and, more in general, from 100.degree. to 200.degree. C.
According to this technique, the reaction rate is generally very low. However it can be raised by increasing the temperature. Such increase in temperature causes, however, the loss of low molecular weight products owing to entrainment by the fluorine which bubbles in the liquid product. Due to the reasons mentioned hereinabove, therefore it is not possible, by operating according to this technique, to neutralize low molecular weight products, such as, for example, perfluoroalkyls of type R.sub.f COF(R.sub.f =--CF.sub.3, --C.sub.2 F.sub.5, --C.sub.3 F.sub.7 and the like) or low molecular weight perfluoropolyethers, such as those, for example, which are prepared through the known process of degrading perfluoropolyethers by means of Lewis acids.
Alternative technological solutions such as fluorination under pressure are hazardous and difficult to carry out owing to the characteristics of the halogen. In most of cases, the fluorination at high temperatures does not permit to achieve a complete neutralization, unless very high reaction times, which are not consistent with a usual commercial-scale process, are employed. In a process of such type, the profitability limit is generally bound to the obtainment of a neutralization degree of 5.10.sup.-4 m.eq. COF/g of fluorinated product, such value representing in practice the lowest sensitivity limit in the acidimetric analysis.
On the other side, the removal of the end groups of the acid fluorine type by means of KOH at temperatures ranging from 130.degree. to 250.degree. C., optionally to be carried out in an autoclave for the low molecular weight products, involves the introduction of hydrogen atoms into the end groups, what gives rise to formation of undesirable group of type --CF.sub.2 H, --CFH--CF.sub.3.